Christian Schubert

Quantum tests of the Einstein Equivalence Principle with the STE-QUEST space mission

We present in detail the scientific objectives in fundamental physics of the Space-Time Explorer and QUantum Equivalence Space Test (STE-QUEST) space mission. STE-QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing equivalence principle tests in the quantum regime, i.e. using quantum atomic wave interferometry. Although STE-QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and proposals to take advantage of the STE-QUEST experience.

Self-alignment of a compact large-area atomic Sagnac interferometer

We report on the realization of a compact atomic Mach?Zehnder-type Sagnac interferometer of 13.7?cm length, which covers an area of 19?mm2 previously reported only for large thermal beam interferometers. According to Sagnacs formula, which holds for both light and atoms, the sensitivity for rotation rates increases linearly with the area enclosed by the interferometer. The use of cold atoms instead of thermal atoms enables miniaturization of Sagnac interferometers without sacrificing large areas. In comparison with thermal beams, slow atoms offer better matching of the initial beam velocity and the velocity with which the matter waves separate. In our case, the area is spanned by a cold atomic beam of 2.79?m?s?1, which is split, deflected and combined by driving a Raman transition between the two hyperfine ground states of 87Rb in three spatially separated light zones. The use of cold atoms requires a precise angular alignment and high wave front quality of the three independent light zones over the cloud envelope. We present a procedure for mutually aligning the beam splitters at the microradian level by making use of the atom interferometer itself in different configurations. With this method, we currently achieve a sensitivity of .

Species-selective lattice launch for precision atom interferometry

Long-baseline precision tests based on atom interferometry require drastic control over the initial external degrees of freedom of atomic ensembles to reduce systematic effects. The use of optical lattices (OLs) is a highly accurate method to manipulate atomic states in position and momentum allowing excellent control of the launch in atomic fountains. The simultaneous lattice launch of two atomic species, as required in a quantum test of the equivalence principle, is however problematic due to crosstalk effects. In this article, we propose to selectively address two species of alkalines by applying two OLs at or close to magic-zero wavelengths of the atoms. The proposed scheme applies in general for a pair of species with a vastly different ac Stark shift to a laser wavelength. We illustrate the principle by studying a fountain launch of condensed ensembles of 87Rb and 41K initially co-located. Numerical simulations confirm the fidelity of our scheme up to few nm and nm s−1 in inter-species differential position and velocity, respectively. This result is a pre-requisite for the next performance level in precision tests.

Future Gravity Field Satellite Missions

The project “Future Gravity Field Satellite Missions” (FGM) was a logical consequence of two previous phases in Theme 2 “Observation of the System Earth from Space” in the BMBF/DFG (Federal Ministry of Education and Research/German Research Foundation) Research and Development Programme GEOTECHNOLOGIEN.

High resolution rotation sensor based on cold Rubidium atoms

We report on our compact transportable cold atom inertial sensor for precision sensing of rotations. The sensor consists of a dual Mach-Zehnder type atom interferometer operating with laser-cooled 87Rb. Raman processes are employed to coherently manipulate the matter waves. We present the latest inertial sensitive interferometer measurements and discuss the road map to reach the full potential of the sensor featuring a sensitivity of a few nrad/s/√Hz.